If an Orc invests in the "Suppression of Summoning" skill, then the impact of his units on the Hive will be significantly reduced... And if he has "Frightful Roar," he can instantly drive the Ents away from their super-defensive position. How do you deal with that?

That's rough. :) I didn't know about the Roar. I don't play as Orcs myself, only against them. Well, then he'll take out the archers, what can you do. But he won't take them out immediately. First, I attack first, and my units will be standing in front of him. Second, the Ents immobilize, so he needs to get through more than just one stack to reach my archers. Third, I'll have summoned creatures, so I can hide behind them. Fourth, Suppression won't save him: I have Wisdom, Druid Channeling, Summoning magic, plus artifacts that boost Knowledge, plus two skills that enhance the summoning of elementals, and a skill that enhances resurrection. So, the Hive will be less effective, but that's not so important. I only need it at the beginning of the battle, for the first three turns. Then it's a different story - summons, resurrections, defense.